The present invention relates to a contact key switch used as an input key for an electronic instruments such as a telephone, a calculator, and an AV instrument, or a automobile le such as a power window and a remote controlled door mirror, and a method for its manufacture.
As a rule, the rubber-like elastic key pad of the main body of a contact key switch is manufactured using as a material an insulating rubber-like elastic body represented by materials such as a natural rubber, synthetic rubber, or thermoplastic elastic body, by processing with various methods such as compression molding, injection molding, etc. Among the rubber-like elastic body, silicon rubber is frequently used for having many characteristics, such as electric insulation, low temperature resistant, heat proof, chemical resistance, precision molding ability, and resilience elasticity, necessary for a contact key switch.
A contact portion is exemplified by those molded integrally with an electroconductive chip on the contact portion of the key pad in a given shape by mixing carbon black and metal powder in a rubberlike elastic material, those formed by preparing a layer of electroconductive ink on the contact portion by screen printing or pad printing after previous making the main body of the contact key switch, and those molded integrally after preparing the electroconductive chip by punching a layering body, that is made by layering a metal layer plated a metal plate on a rubber layer, in a given shape.
However, said contact portion has been made by mixing carbon black and metal powder, which are electroconductive media, in an elastic material or ink. Therefore, compounding a large quantity of an electroconductive medium yields some 10 ohms or higher of a contact resistance, not allowing a use suitable for the low contact resistance of some ohms or lower.
In addition, the contact portion of a contact switch made by plating of a metal on a rubber layer is, as described in Japanese Patent Publication 06(1994)-93335 and Japanese Patent Laid-Open 08(1996)276435, is made of a metal, and suitable for the use for a low resistance. However, silicon as the material of the keypad is normally difficult to adhere to a metal as known from the use as a release agent. Therefore, adhesive and adhering procedure should be used by selection to make adhesion of both materials possible. On the other hand, both sides of the electroconductive chip have consisted of a metal layer and an insulating rubber layer. Therefore, the metal layer should be contact with the-mold surface at insertion of the mold in molding step. This step makes the efficiency of manufacture worse and cost higher.
To solve the aforementioned problem, the present invention provides a contact key switch usable for a low resistance by making the surface of contact portion of contact switch with electroconductive woven fabric or electroconductive nonwoven.
The material of the rubber part of the main body of the contact switch and layered body is, as used as the contact switch, not specially restricted if having a high resilience elasticity, however, preferably an insulating rubber-like elastic body represented by a synthetic rubber selected from at least any one of natural rubber, ethylenepropylene rubber, silicon rubber, butadiene rubber or a thermoplastic elastic body selected from at least any one of styrene, esters, olefins, urethanes, and vinylated compounds.
On the other hand, the constituent of the electroconductive woven fabric or electroconductive nonwoven fabric is not specially restricted if at least one of warp fibers or woof fibers is consisted of electroconductive fibers.
Further, the present invention provides a contact key switch excellent in characteristics such as !ow temperature resistant, heat-proof, chemical resistance, precision molding ability, and resilience elasticity, by using silicon rubber for a rubber-like elastic body.
Furthermore, the present invention provides a contact key switch usable for a low resistance by using material selected from carbon fiber and metal fiber for an electroconductive woven fabric or an electroconductive nonwoven fabric.
According to the present invention, carbon fibers composing the electroconductive woven fabric or the electroconductive nonwoven fabric is selected from fiber constitution of number of wales of 10 to 30 per 25 mm and filament number of 1000 to 6000 in the electroconductive woven fabric and carbon mass rate of 0.03 to 2.5 g per Cm3 in the electroconductive nonwoven fabric. A smaller number of fiber constitution than that of respective number ranges increases surface resistance by invasion of unvulcanized rubber, in the surface of layered contact portion due to large opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric. A larger number of fiber constitution than that of respective number ranges easily allows surface dissociation by lowered holding performance of vulcanized rubber and fibers caused by no invasion of unvulcanized rubber between fibers due to small opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric.
The method for manufacture of carbon fibers is not specially restricted, and can be selected from fibers prepared by carbonizing through heat treatment of fibers made by spinning of an organic fibers such as rayon and polyacrylonitrile and purified petroleum pitch in an inert gas atmosphere.
The material of metal fiber is not specially restricted, and may be fibers-such as gold, gold alloy, silver, copper, copper alloy, iron, nickel, brass, and when corrosible material is used, those of which the entire surfaces has been plated with a material, such as gold or gold alloy, not easily corrosible.
The layered contact portion is manufactured by penetrating unvulcanized rubber into the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric to harden and make a layered body, and by punching the layered body in a given shape.
The layered body made of the rubber layer and the electroconductive woven fabric or the electroconductive nonwoven fabric, of the present invention, is manufactured by layering the electroconductive woven fabric or the electroconductive nonwoven fabric on the unvulcanized rubber to subject to compression molding.
The layered body made of the rubber layer and the electroconductive woven fabric or the electroconductive nonwoven fabric, of the present invention, is manufactured by layering evenly the unvulcanized rubber on the electroconductive woven fabric or the electroconductive nonwoven fabric using a roll or a blade, if necessary, by further layering the electroconductive woven fabric or the electroconductive nonwoven fabric on the unvulcanized rubber, and by using a hardening furnace with far infrared rays, near-infrared rays, or heat air.
According to aforementioned method, the unvulcanized rubber is hardened after penetrating into the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric to allow easy formation of the layered contact portion. Thus, selection and use of an adhesive and adhesion process is not necessary.
The condition of the unvulcanized rubber of the present invention is not restricted to either a liquid form or a solid form. However, when the unvulcanized rubber is evenly layered on the electroconductive woven fabric or the electroconductive nonwoven fabric by using a roll or a blade, the liquid form is preferable for easy penetration into the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric.
In the use of silicon rubber for the rubber layer, if silane coupling agent is applied to the electroconductive woven fabric or the electroconductive nonwoven fabric, if necessary, the holding performance of the electroconductive woven fabric or the electroconductive nonwoven fabric is increased. A silane coupling agent is used broadly in order to improve reactivity with the material which is hard to stick to an end usually. For example, there are vinyl-trimeto-xylane, amino-silane, and these are appropriately selected according to the material. In addition, the rubber layer is not restricted to insulating or electroconductive rubber layer. However, if electroconductive rubber is used, the contact resistance of the contact portion shows a tendency to fall to a lower value. The layered contact portion is formed by punching the layered body in a given shape. The layered contact portion is engaged to the contact part of the mold of the rubber-like elastic key pad to fit the surface of the electroconductive woven fabric or the electroconductive nonwoven fabric to the mold, followed by integrated molding by inserting the rubber-like-elastic material in the mold.
The layered body made of the rubber layer and the electroconductive woven fabric or the electroconductive nonwoven fabric, of the present invention, is manufactured by putting the electroconductive woven fabric or the electroconductive nonwoven fabric on the mold for injection molding, extruding the thermoplastic elastic body to the mold, and seizing the melted thermoplastic elastic body to the electroconductive woven fabric or the electroconductive nonwoven fabric or penetrating to the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric.
Layering the electroconductive woven fabric or the electroconductive nonwoven fabric on both sides of the rubber layer causes both sides to have electroconductivity in the layered contact portion. Therefore, a jig or an apparatus for identifying the side of the layered contact portion is not necessary for insertion of the layered contact portion in the contact part of the mold to allow efficient manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.